Swallowdale is the second book in the Swallows and Amazons series by Arthur Ransome. It was published in 1931. In this book, camping in the hills and moorland country around Ransome's Lake in the North features much more prominently and there is less sailing. A significant new character, Maria Turner, the Blacketts' Great Aunt, is introduced.

Ransome was living in the Lake District and he drew on his experiences and memories of encounters over many years with the local farming community. Ransome had often climbed Old Man of Coniston and in the book, this becomes the children's Kanchenjunga. Expeditions to Kanchenjunga in the Himalayas had been much in the news while Ransome was writing the book.

Returning to Wild Cat Island for their second summer holiday by the Lake, the Swallows find the Amazons and Captain Flint suffering from "native trouble". Great Aunt Maria has come to stay, and she is a stickler for "proper" behaviour; demanding that the Amazon pirates act like "young ladies", and restricting their time.

Despite this, Nancy and Peggy escape the Great Aunt and arrange a rendezvous, but on the way the Swallow hits Pike Rock and sinks. All are saved and the boat salvaged, but she needs repairing, so camping on the island is impossible."Captain" John of the Swallows learns some valuable life lessons about following his instincts while commanding a ship, and has time to reflect on the accident while he fashions a new mast for Swallow. Fortunately an alternative appears to replace camping on Wildcat, as Roger and Titty find a beautiful hidden valley, Swallowdale, up on the moors above the lake.

The Swallows discover a secret cave in Swallowdale, a trout tarn, the "knickerbockerbreaker", and enjoy new adventures of lakeland life. They meet local woodcutters and farmers, see a hound trail, and trek across the moors. The Amazons are only able to escape at intervals, and are punished for getting home late by being made to memorize and recite poetry. Eventually the Great Aunt leaves and the Swallows and Amazons mount an expedition to sleep under the stars on the "summit" of nearby commanding hill "Kanchenjunga".

Next morning, Roger and Titty return to Swallowdale following trails through the bracken across the moor, while the elders ferry the Amazons' camping gear by boat. Both parties get lost in a thick and sudden fog. After it lifts the elders arrive only to find an empty camp. Titty arrives late after hitching a ride with some woodsmen, and explains that Roger sprained his ankle, and will be spending the night with Old Billy, the charcoal burner. The next day the injured Roger is carried back to the camp on a stretcher.

The Swallow is finally repaired, and the book ends with a race and a feast, followed by a return to Wild Cat Island.